The present invention relates to a band combining filter. More particularly, but not exclusively, the present invention relates to a band combining filter comprising a plurality of filter sections connected together in cascade along with a phase shifter, the filter sections including resonators and at least one of the filter sections being a high Q filter section.
Band combining filters are known. Such band combining filters can include a plurality of resonators. In the case of a rapid transition from passband to stopband the resistive loss of the resonators causes a roll off of the insertion loss into the passband. In order to meet typical rejection requirements unloaded Qs of greater than 20,000 are required resulting in the necessity, at microwave frequencies to use dielectric resonators for all of the cavities resulting in a physically large heavy and expensive filter.
The present invention seeks to overcome the problems of the prior art.